I. Field of the Invention
The present invention relates to sample sites to be coupled via a catheter or the like to a patient's circulatory system and through which a sample of the patient's blood may be withdrawn.
II. Description of the Prior Art
Sample sites typically include a fluid cavity in line with tubing connected to a patient's circulatory system. Blood may be withdrawn through the sample site by inserting a needle into the fluid cavity through a latex plug in the sample site and withdrawing the fluid in the cavity.
An exemplary system which may advantageously employ a sample site for withdrawing blood is a blood pressure monitoring system in which a catheter inserted into a patient's blood vessel is connected via tubing to a blood pressure sensor, and a stopcock, which either connects the tubing to a supply of saline solution or a reservoir. A sample site may be included in-line with the tubing midstream between the patient and the stopcock to facilitate blood sampling without an additional needle puncture to the patient.
When the tubing is connected through the stopcock to the saline source, the sensor is in fluid communication with the patient's circulatory system to sense the patient's blood pressure. When it is desired to take a sample of the patient's blood, rather than puncturing the patient with another needle, the sample site may be used. To this end, the stopcock is turned to disconnect the saline source from the patient's circulatory system and instead couple the patient's circulatory system to the reservoir. Saline will flow away from the patient and into the reservoir as the patient's blood flows through the tubing and into and through the sample site. Thereafter the needle of a syringe is inserted into the sample site and blood is withdrawn therefrom with the syringe. The needle is then removed from the sample site after which the stopcock is turned to disconnect the patient's circulatory system from the reservoir, reestablishing the connection between the patient's circulatory system and the saline source so as to reestablish the blood pressure monitoring function.
When using a sample site as in the above-described system, it is desirable that whole blood be removed from the patient through the sample site. That is, it is desirable that the blood removed through the sample site not be mixed with any other fluid, such as the saline solution normally present in the sample site during blood pressure monitoring. However, with previously existing sample sites, not all of the saline may be displaced from the cavity during a sampling operation leading to diluted blood samples rather than whole blood samples as is desired.